On the Design Details of SS/PBCH, Signal Generation and PRACH in 5G-NR

Abstract

The 3rd Generation Partnership Project (3GPP) specification of the fifth generation (5G) New Radio (NR) allows for a highly scalable and flexible radio access technology to cater to network operators with different requirements. Such scalability and flexibilities in network configurations inevitably translate to complications in the design and implementation of 5G-NR systems. Radio access in 5G-NR is much more complex and involved than its predecessor, 4G long term evolution (LTE) and LTE-Advanced technology. Therefore, the 5G-NR specifications turn out to be quite dense. Specifically, the specifications are concise, design motivations rarely explained, and the information can be convoluted or distributed across several documents. Moreover, there are several key design details associated with the access layer procedures for any given physical layer channel, which are often omitted in the specifications. For example, design motivation aspects of initial access channels or signal generation can be quite difficult to follow or understand in 5G-NR. In this paper, all the design details associated with initial access channels and signal generation in 5G-NR specifications are laid out. The contributions of the paper are three folds. First, the design details and justifications associated with both downlink and uplink access channels are presented along with signal generation details. Secondly, receiver design aspects of NR PRACH short formats are discussed. Lastly, PRACH receiver implementation aspects and performance reports from different network operators are presented and compared with 3GPP specified Radio Performance and Protocol aspect requirements 1 for millimeter wave (mmW) access. The work in this paper is of significant value to researchers and system engineers looking to design and build initial access algorithms as part of 5G NR systems.

On the Structured Design Methodology of Effective PRACH Detection: Multi-Stage Thresholding Perspective

“…In conjunction with the stable transmission of the uplink synchronization signal with good correlation properties, the design of highly reliable detection for the NR PRACH preamble is crucial for achieving a successful initial RACH process beyond LTE PRACH preamble detection [5].. For this purpose, the PRACH preamble detector typically makes use of a Power Delay Profile (PDP) which is a consecutive series of correlation power according to timing offset [6], [7]. Therefore, PDP refinement is one of the critical ingredients for effective PRACH preamble detection.…”

Implementation and analysis of 5G network identification operations at low signal-to-noise ratio

“…In this situation, a certain time delay occurs on the receiving side due to the deviation of the samples from the optimal values. This process is accompanied by a phase offset that is proportional to the timing offset and subcarrier indices [11]- [13]. The timing error can be caused by a mismatch between the transmitter and receiver frequencies due to Doppler shift resulting in intersymbol interference between the OFDM carriers.…”

Simplification of DFT and IDFT in PRACH

“…Physical random access channel (PRACH) [1] has been widely deployed in cellular systems, including wideband code division multiple access (WCDMA), long term evolution (LTE) and new radio (NR), and its signal generation [2] is a topic of concern. In PRACH, the random access preamble is a cyclic shifted ZC (Zadoff‐Chu) sequence, as follows: $$$$\begin{equation}{x_{u,v}}\left( n \right)\ = {x_u}\ \left( {\left( {n + {C_v}} \right)mod{L_{{\mathrm{RA}}}}} \right)\end{equation}$$$$ $$$$\begin{equation}{x_u}\ \left( i \right) = {e^{ - j\frac{{\pi ui\left( {i + 1} \right)}}{{{L_{{\mathrm{RA}}}}}}}}\ ,\ i\ = \ 0,1, \ldots ,{L_{RA}} - 1\end{equation}$$$$where C v is the shifted value, j is the imaginary unit, L RA and u are the length and root index of the ZC sequence, respectively.…”

“…Introduction: Physical random access channel (PRACH) [1] has been widely deployed in cellular systems, including wideband code division multiple access (WCDMA), long term evolution (LTE) and new radio (NR), and its signal generation [2] is a topic of concern. In PRACH, the random access preamble is a cyclic shifted ZC (Zadoff-Chu) sequence, as follows:…”